Reliable forecasting of extreme weather: new study supports improvement of climate models

In order to better prepare for disasters, it is important to be able to better predict the duration of weather periods. Photo: arhendrix - stock.adobe.com

Torrential rainfall such as that recently experienced in Spain is just one form of extreme weather event that is becoming more frequent as a result of climate change. With catastrophic consequences. Storms, droughts and heatwaves are also increasing in intensity. One of the decisive factors for the damage they cause is their duration. However, it is not yet possible to reliably predict this using current climate models. A research team led by Albert Ossó from the Wegener Center at the University of Graz has now succeeded in identifying some of the causes of this modelling problem. The new findings, which have been published in the journal Geophysical Research Letters, might help to improve the accuracy of climate models and thus forecasts of extreme weather events in Europe.

According to estimates by the European Environment Agency, between 85,000 and 145,000 deaths and economic losses of half a trillion euros have been caused by extreme weather events over the last forty years. "In order to better prepare for the future, it is crucial to understand how the meteorological patterns underlying these events will change," says Albert Ossó, researcher at the Wegener Centre for Climate and Global Change at the University of Graz.

In his most recent study, he and his team focused on the Summer North Atlantic Oscillation (SNAO). This has a significant influence on European weather in the warm season. "The SNAO describes a north-south shift of the jet stream, a strong wind field over the North Atlantic. In the so-called positive phase, the jet stream shifts northwards and directs more Atlantic storms towards northern Europe and Scandinavia. This generally leads to above-average humid weather in these regions, while fewer storms occur in Central Europe, which tends to be drier. In the negative phase, the pattern reverses and the wetter conditions shift southwards to Central Europe," explains Ossó.

If the SNAO remains in a certain phase for a longer period of time, the corresponding weather continues, which can result in droughts or flooding due to unusually heavy rainfall. "For reliable predictions of how often these extended dry or wet periods occur - and how long they will last in a warmer future climate - we first need models that accurately capture these patterns in today's climate," says Ossó. However, this is not the case. "We have found that the simulations tend to overestimate the duration of such periods in summer," says the researcher. In their current study, the scientists show the reasons for this modelling problem and thus lay the foundation for improving future climate predictions.

Publication:
Ossó, A., & Ennemoser, F. (2024). Persistent Summer North Atlantic jet variability: Dynamical feedbacks and model‐observation discrepancies. Geophysical Research Letters, 51, e2024GL109788.
https://doi.org/10.1029/2024GL109788

Gudrun Pichler